So for this expression, you are plugging the value of f(a) into the a variable of g(a).
[tex]g(f(a))=3(a^2+3)-1[/tex]
Firstly, distribute 3 to (a^2 + 3):
[tex]g(f(a))=3a^2+9-1[/tex]
Next, combine like terms and your answer will be:
[tex]g(f(a))=3a^2+8[/tex]
